Patchwork [PULL,07/30] qcow2: Flush image after creation

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Submitter Kevin Wolf
Date Oct. 31, 2013, 3:48 p.m.
Message ID <>
Download mbox | patch
Permalink /patch/287522/
State New
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Kevin Wolf - Oct. 31, 2013, 3:48 p.m.
From: Max Reitz <>

Opening the qcow2 image with BDRV_O_NO_FLUSH prevents any flushes during
the image creation. This means that the image has not yet been flushed
to disk when qemu-img create exits. This flush is delayed until the next
operation on the image involving opening it without BDRV_O_NO_FLUSH and
closing (or directly flushing) it. For large images and/or images with a
small cluster size and preallocated metadata, this flush may take a
significant amount of time and may occur unexpectedly.

Reopening the image without BDRV_O_NO_FLUSH right before the end of
qcow2_create2() results in hoisting the potentially costly flush into
the image creation, which is expected to take some time (whereas
successive image operations may be not).

Signed-off-by: Max Reitz <>
Reviewed-by: Eric Blake <>
Reviewed-by: Benoit Canet <>
Signed-off-by: Kevin Wolf <>
 block/qcow2.c | 10 ++++++++++
 1 file changed, 10 insertions(+)


diff --git a/block/qcow2.c b/block/qcow2.c
index 01269f9..6e5d98d 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1584,6 +1584,16 @@  static int qcow2_create2(const char *filename, int64_t total_size,
+    bdrv_close(bs);
+    /* Reopen the image without BDRV_O_NO_FLUSH to flush it before returning */
+    ret = bdrv_open(bs, filename, NULL,
+                    BDRV_O_RDWR | BDRV_O_CACHE_WB, drv, &local_err);
+    if (error_is_set(&local_err)) {
+        error_propagate(errp, local_err);
+        goto out;
+    }
     ret = 0;